1. Field of the Invention
The present invention relates generally to a functionalized membrane and a matrix to purify nucleic acids, and particularly to a method for purifying the nucleic acids by means of such membranes and matrices.
2. Discussion of Related Art
Membranes useful to purify nucleic acids are commonly known from, for example, U.S. Pat. No. 5,438,128. The membranes are typically a porous polymer made of polypropylene or nylon, and are functionalized with ion-exchange groups. At low ion concentrations, the functionalized membranes bind to ionized nucleic acids, and at high ion concentrations the bound nucleic acids are eluted.
The known porous membranes are used in methods or kits to purify nucleic acids. In general, the raw material containing the nucleic acids, which may have to be pre-purified, is in a low ionic-concentration binding buffer solution and is aspirated or pressed through the membrane. When moving through the membrane, the nucleic acids are selectively bound by the ion-exchange groups to the membrane surface. In a subsequent step, the membrane is washed to separate non-specifically bound contaminants. Optionally, the wash is accomplished using a buffer of higher ionic strength. The elution of the bound nucleic acids then takes place in a further stage using a buffer of still higher ionic strength.
A feature of the membranes of the present invention is that the membranes that are useful to purify nucleic acids have surfaces that are functionalized with deprotonatable groups. Such membranes are described by ULBRICHT & RIEDEL in BIOMATERIALS 19 (1998), pp 1,229–1,237 only in conjunction with protein immobilization. A goal of the invention, namely purifying nucleic acids, was not mentioned or implied by the reference.
Unfortunately, because of the high salt concentration the eluate must be purified in almost all cases before it may be processed further. The purification step uses, for example, ethanol precipitation or dialysis.
As disclosed in U.S. Pat. No. 5,693,785, hydroxylated silica beads are sometimes used to purify nucleic acids. When the beads are used, a chaotropic buffer is required to assure adequate binding of the DNA to the silica beads. In the absence of chaotropic binding buffers, binding takes place only when the surface is strongly positively charged.